The present invention relates to computer disk drive transducer heads. In particular, the present invention relates to transducer heads having an inductive write head and a magnetoresistive or a giant magnetoresistive read head.
Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks, divided into sectors. Information is written to and read from a disk by a transducer head, mounted on an actuator arm capable of moving the transducer head radially over the disk. Accordingly, the movement of the actuator arm allows the transducer head to access different tracks. The disk is rotated by a spindle motor at a high speed, allowing the transducer head to access different sectors on the disk.
A typical computer disk drive is illustrated in FIG. 1. The disk drive, generally identified by reference numeral 20 includes a base 24 and magnetic disks 28 (only one of which is shown in FIG. 1). The magnetic disks 28 are interconnected to the base 24 by a spindle motor (not shown) mounted within or beneath the hub 32, such that the disks 28 can be rotated relative to the base 24 Actuator arm assemblies 36 (only one of which is shown in FIG. 1) are interconnected to the base 24 by bearings 40, such that they can be moved radially with respect to the magnetic disks 28. The actuator arm assemblies 36 include transducer heads 44 (only one of which is illustrated in FIG. 1) at a first end, to address each of the surfaces of the magnetic disks 28. A voice coil motor 48 pivots the actuator arm assemblies 36 about the bearings 40, to radially position the transducer heads 44 across the surfaces of the magnetic disks 28. The voice coil motor 48 is operated by a controller 52 that is in turn operatively connected to a host computer (not shown). By changing the radial position of the transducer heads 44 with respect to the magnetic disks 28, the transducer heads 44 can access different data tracks or cylinders 56 on the magnetic disks 28.
A typical transducer head contains functionally separate write and read heads, or elements, that are integrated into a unitary, thin film structure. A conventional thin film transducer head 100 is illustrated in FIGS. 2 and 3, and generally includes a write head 104 and a read head 108.
The write head 104 is usually what is known as an inductive head. Where such heads are constructed from ferrite material, they are known as ferrite heads. The write head 104 generally includes a yoke of magnetically conductive material formed from a write pole 112 and a shared shield 116. A coil of electrically conductive wire 118 is wrapped about a portion of the yoke, and the ends of that coil are connected to a current source (not shown). During a write operation, current is introduced to the coil in a first direction. The electrical current through the coil produces a magnetic field within the yoke. At a gap 120 formed between an end of the write pole 112 and an end of the shared shield 116, the magnetic field spreads out because the magnetic permeability of the gap is less than that of the yoke itself. The gap 120 is positioned so that it is in close proximity to the magnetic disk, allowing some of the magnetic field to pass through the disk and magnetize a portion of the disk in a particular direction. In a typical disk drive for use in a digital computer, a xe2x80x9conexe2x80x9d is coded by reversing the direction in which the disk is magnetized from one portion of a track to the next. This is done by reversing the direction of the current in the coil. A zero is indicated by the absence of a change in magnetic polarity. Of course, these conventions could be reversed.
The read head 108 in a disk drive operates by sensing the magnetic flux transistions encoded in the disk by the write operation. One method of sensing such transistions is with a magnetoresistive head. Such a head is comprised of material that changes its electrical resistance when it is exposed to a magnetic field. Magnetoresistive heads have come into wide use in disk drive systems because they are capable of providing high signal output. High signal output is important, because the magnetic fields produced in the disks by the write operation are very small. In addition, the high signal output of the magnetoresistive head allows the data on the disk to be densely packed, allowing the disk drive to have a high storage capacity.
Magnetoresistive read heads generally include a strip of magnetoresistive material 124 held between two magnetic shields. In the conventional transducer head illustrated in FIGS. 2 and 3, the magnetic shields are formed from the shared shield 116 and a read shield 128. Each end of the strip of magnetoresistive material 124 is connected to a conductor (not shown). The conductors are in turn connected to a current source (not shown). Because the electrical resistance of the magnetoresistive material varies with the strength and direction of an applied magnetic field, magnetic flux transistions result in changes in the voltage drop across the magnetoresistive strip. These changes in the voltage drop are sensed and then converted into a digital signal for use by the host computer.
In order to sense the transistions between the small magnetic fields and thus retrieve data from the magnetic disk, the magnetoresistive read head 108 is held in close proximity to the track containing the desired information. The disk 28 is rotated under the head 44, and flux transitions read by the head 44 are interpreted as a binary xe2x80x9conexe2x80x9d, as described above. The magnetic shields on either side of the magnetoresistive material 124 limit the effect of magnetic flux transitions adjacent to or in the proximity of the precise area of the track from which information is to be retrieved. Often, one pole of the inductive write head also serves as part of the shield. This shared shield is typically about 1-3 xcexcm thick.
In FIG. 3, a typical transducer head 100 having a write head 104 and a read head 108 is illustrated in plan view. As described above, the write head 104 generally includes a write pole 112 and a shared shield or pole 116 with a write gap 120 therebetween. The read head 108 generally includes the shared shield 116, a magnetoresistive element 124, and a read shield 128. Such heads are typically manufactured using thin film layering techniques.
The strength of the magnetic field produced in the read head 108 from the data written to the storage disk 28 is small (from 10-50 oersteds). However, while writing the magnetic field that must be produced by the write head to encode the data by magnetizing the disk is relatively large (as much as several thousand oersteds). The strong magnetic field produced by the inductive write head during a write operation affects the operation of the magnetoresistive read head. The strength of the magnetic field produced in the read head 108 during a write operation can be as strong as several hundred oersteds. This strong magnetic field is believed to, at times, force an unstable magnetic domain state in the shield and/or permanent magnet structures of the read head, since conventional read heads are only designed to sense magnetic fields of about 50 oersteds. Accordingly, following a write operation, the magnetoresistive head may undergo write induced instabilities when the magnetic domain state of the shields and/or permanent magnet structures revert to their normal state. When the reversion occurs, the read head cannot reliably read information from the storage disk.
Because it is necessary to maintain the position of the transducer head over the disk with high accuracy, the transducer head must be able to read servo sector information embedded periodically about the disk both during, and following, write operations. Where the read transducer is unable to confirm the correct position of the transducer head relative to the storage disk, the write operation must be terminated. After such a servo error, the write operation must be suspended until the disk has traveled through one complete revolution and the sector where the write operation was interrupted is reached again, so that writing may be xe2x80x9cretriedxe2x80x9d. The performance of the drive, which is required to write information with high speed and high accuracy, can be significantly diminished by such errors. Write-induced magnetic instabilities in the read head also affect the manufacturing efficiency of disk drives, as drives that exhibit a predetermined number of write-instability related servo errors during post-manufacturing testing cannot be shipped to consumers.
Typically, the read and write heads of a transducer are aligned so that they are positioned over the same track (see FIG. 3). The distance between the read and write heads of a transducer head are typically kept as small as possible in a downtrack direction in order to limit the skew of the heads relative to the data tracks. However, because the read and write elements of a transducer head are separate from one another in a downtrack direction, they are generally unable to follow the same path over the disk. The amount by which the paths of the read and write heads differ, or the skew, depends on the radial position of the transducer head over the disk. This presents a problem during write operations, during which the read head is used to position the transducer in the center of the data track onto which information is to be written, because the write head will not be centered in the track. In order to correct this problem, disk drives often move the transducer head immediately after reading the servo data to correctly position the write head. This adjustment is known as xe2x80x9cmicrojogging.xe2x80x9d In general, xe2x80x9cicrojogxe2x80x9d operations have generally been limited to distances of less than one track width, or less than about 2 xcexcm.
Another solution for limiting the skew of the read and write elements relative to the data tracks, and thus to limit the amount of microjog, is to stagger the read and write elements laterally with respect to the data track. The optimum amount of lateral offset between the read and write elements depends on the geometry of the particular disk drive assembly, but is generally less than one track width, or less than about 2 xcexcm. For example, U.S. patent application Ser. No. 08/798,606, now U.S. Pat. No. 5,978,168, issued Nov. 2, 1999, and which is assigned to the assignee of the present application, discloses a lateral or cross-track offset between the read and write elements relative to the data tracks to reduce skew and to therefore reduce the amount of microjog necessary to center the write element over the data track.
While these existing disk drive designs do offset the read and write elements from one another, they fail to solve the problem of write induced instabilities in the read element since the spacing between the write and read elements is small, usually less than 2 or 3 microns.
It would be advantageous to provide a transducer head having a read element that is capable of accurately reading servo information in close temporal proximity to a write operation. In addition, it would be advantageous to provide a system that does not produce spurious or unreliable signals from the read element following a write operation. Furthermore, it would be advantageous to produce a transducer head that is reliable and inexpensive to manufacture.
In accordance with the present invention, a computer disk drive transducer head is provided having spatially separated read and write heads. The read head may be offset from the write head either in a cross-track direction, in a downtrack direction, or both in a cross-track and in a downtrack direction. The transducer head design of the present invention operates by spacing the read head away from the write head, and thereby reducing the amount of magnetic flux produced during write operations that passes through or in close proximity to the read head. In particular, the read and write heads are separated sufficiently that the strength of the magnetic field seen by the read head during write operations is about equal to the strength of the magnetic field of the magnetic storage disks seen by the read head.
According to a first embodiment of the present invention, the transducer head of the present invention generally includes a magnetoresistive read head spaced apart from an inductive write head by a shared shield or pole, and laterally offset from the center line of the write head so that the center of the read head and the center of the write head are separated by an amount sufficient that the strength of the magnetic field in the read head during a write operation is about zero. The transducer head, according to this embodiment, utilizes the shared pole both as a shield for the magnetoresistive read head and as a pole of the inductive write head.
In a second embodiment, the transducer head of the present invention includes an inductive write head and a magnetoresistive read head that are not integral with each other. The separate read and write heads may be positioned such that they are laterally offset from each other. According to this embodiment, because the read and write heads are not integral with one another, they may be placed in any spatial relationship to one another. In a preferred embodiment, the read head is positioned so that it is spaced apart from the write head a distance sufficient that the strength of the magnetic field in the read head during a write operation is about zero.
According to a third embodiment of the present invention, a shared shield between the write gap and the magnetoresistive head is thick enough to space the read head and the write head sufficiently far apart that the strength of the magnetic field in the read head during a write operation is about zero. This embodiment of the invention allows for the magnetoresistive head to be spaced widely from the write gap of the inductive write head.
Based on the foregoing summary, a number of salient features of the present invention are readily discerned. A computer disk drive transducer head is provided with improved performance. In particular, a transducer head is provided in which disruption to the read head""s ability to reliably retrieve information from the storage disk following or during a write operation is reduced or eliminated.